Devices and methods for testing the performance of high-pressure fuel injectors, such as those commonly used in diesel engines, are known. Generally, the testing devices or methods are used to: 1) evaluate the spray pattern of a fluid discharged from the injector nozzle; 2) measure the flow rate of fluid from the injector; 3) determine the lubricating or fouling characteristics of the fluid in the fuel injector; or 4) measure the pressure of fluid in the fuel injector. Because of environmental requirements for cleaner burning diesel engines, control of the fluid pressure, and therefore measurement of fluid pressure near the nozzle outlets of the fuel injector, is important in determining fuel injector performance. The fluid pressure at the nozzle discharge ports impacts fuel combustion patterns and associated formation of by-product air pollutants.
Previously, the pressure of the fluid supplied to a fuel injector is measured at a fuel rail that is downstream of a fuel pump, but before the fuel injector. As shown in FIG. 1, a fuel injector 101 is charged with fluid from a fluid tank 103 by a fuel pump 105 via a fuel rail 107. A pressure sensor 109, such as a strain-gauge pressure sensor, measures the fluid pressure in the fuel rail 107. A pressure regulator 111, which is connected to the fuel rail 107, maintains the pressure in the fuel rail 107 during fuel injector 101 operation.
Prior methods use a strain gauge type pressure sensor to measure fluid pressure. Strain-gauge type pressure sensors suffer from distortion of the pressure measurement due to mechanical stresses induced in high-pressure applications. Placing of pressure sensors in the fluid channels and cavities inside the fuel injector nozzle is known. The mounting of pressure sensors in the fluid channels and cavities within the fuel injector nozzle is difficult, and disrupts both fluid flow patterns and the metering of the fluid.
Accordingly, there is a need for a method of measuring fluid pressure of a fuel injector, which method does not disturb fluid flow patterns or the metering of fluid discharged from the fuel injector.